1. Field of the Invention
This invention relates to a method of manufacturing a sheet metal made poly-V pulley having a plurality of poly-V grooves arranged at a fixed pitch on the outer surface of a peripheral wall of the pulley.
2. Prior Art
In recent years there has been developed a poly-V belt which has replaced a V-belt and which is provided on the inner surface of a belt and along the direction of travel with a plurality of ridges engaging with a plurality of poly-V grooves (about 3.5 mm in width) of poly-V pulleys and various poly-V pulleys for use in the poly-V belt have been developed.
Since the poly-V pulley of the kind described makes it necessary for a plurality of ridges formed on the inner surface of one poly-V belt to engage with the poly-V grooves of the poly-V belt, the accuracy of each poly-V groove of the order of 5/100 mm is rigorously demanded, and consequently the pitch, width, and diameter of each poly-V groove must be finished to close tolerances.
In an attempt to meet such demand, the applicant proposed a method of manufacturing a sheet metal made poly-V pulley (Japanese Patent Application No. 113820/1979, corresponding to U.S. Pat. No. 4,313,323) wherein the peripheral wall of a cup-shaped blank is pressed from outside of the wall by a corrugating roller to bring the wall into a shape of corrugated section in a manner to form ridges alternated with grooves on the outer surface of the peripheral wall, the peripheral wall of the cupshaped blank is subjected axially to compression forming in the state of the outer peripheral edge of an axially movable auxiliary forming roller being inserted into each groove of the corrugated wall, and thereafter the grooves on the outer surface of the peripheral wall are formed into specified poly-V grooves by form rolling adapted to press a finish forming roller against the grooves. According to this method of manufacture, it was possible to greatly improve the accuracy of an article, but the V-grooves obtained or the articles thus produced were not free from variations in accuracy. The proposed method has had something yet to be desired in that it lacked stability of article accuracy.